Yes, as well as playing covers, the band also eats lunch, goes to the can and all the other things common to living people, that doesn’t mean one is not a mathematician or a scuba diver.

If we are going to argue that "this" (A) is not "that" (B) we need to first set up mutually exclusive definitions and show that they are either the same or not the same.

As our definitions in this instance are not mutually exclusive we are wasting our time.

As I said earlier, ask him what a diatonic scale is or how minor tonality differs from a major tonality.
You may want to add that if he wants to be known as a muso, he should learn to play an instrument.